Swaged electrical connection



May 29, 1951 Filed Oct. 20, 1944 S. N. BUCHANAN SWAGED ELECTRICAL CONNECTION 2 Sheets-Sheet 1 INVENTOR S lephen-IVT Buchanan ATTOR EYS y 1951 s. N. BUCHANAN 2,554,813

SWAGED ELECTRICAL CONNECTION Filed Oct. 20, 1944 2 Sheets-Sheet 2 T '33 r m INVENTOR Siephen flffiuchanan @037 XT4Z I NEYS Patented May 29, 1951 UNITED STATES PATENT orrlcs SWAGED ELECTRICAL CONNECTION Stephen 'N. Buchanan, Elizabeth, N. .I., 'assignor ,to Aircraft-Marine Products, Inc., Harrisburg, Pa., a corporation of New Jersey Application October 20, 1944, Serial No. 559,604

6 Claims. 1

This invention relates to electricalconne'ctions and, more specifically, to electrical connections of the type adapted to be permanently impressed onto an electrical connector and conductor by a crimping operation. It is a continuation in part of my earlier applications Serial No. "121,408, .filed December S, 1941, now Patent No. 2,379,567 and Serial No. 474,935, filed February 6, 1943, now abandoned.

Connectors of the type which make mechanical and electrical connection by crimping onto a conductor had been known before these inventions, but such earlier connectors were not without inherent defects or disadvantages. In many of them the bond between the connector and the electrical conductor had not been :sufliciently tight nor permanent to provide for all of the stresses which are imposed subsequently in use,

with the result that "the end of the electrical conductor sometimes pulled loose from the electrical connector. In other terminals the crimped portion which forms the bond between the connector and the conductor has been so deep that the ferrule of the connector and some of the wires of the-conductor were seriously weakened, with the result that the tensile strength of the connection was unsatisfactory. Another defect found in many connections of this type lay in the fact that moisture or other foreign matter could creep into the compressed portion of the connector to promote corrosion of the contact surfaces and thus to lower the electrical conductivity through the connection.

It is an object of the present invention to provide an improved connection wherein the connector is permanently attached to a wire or like member by a crimping operation. Another object is the provision of a crimped connection in which neither the ferrule nor the 'wire is damaged by the crimping. A further object is to provide a permanent electrical connection of high conductivity. Yet a further object is the provision of an improved method of connecting a ferrule to a wire. Still another object is the provision of crimped connectors having shapes and dimensions adapted to concentrate expansive forces in the strongest portions thereof. A further object of the invention is to provide a new and improved solderless connector in which a crimped ferrule is effectively held against bendin and in firm gripping contact with the wires. Other objects will be in part pointed out as the description proceeds and will in part become apparent therefrom.

I have by my present invention demonstrated that an electrical connector of the type provided with a ferrule for connection to a wire, etc., can be permanently attached to an electrical conductor by compression dies with -a permanent low-resistance connection of highest quality, if

the die surfaces which do the compressing are bear a certain relationship to the ferrule to be crimped and so that they first flatten and compress the ferrule ina'predetermined manner and then'coin the metal of the ferrule as hereinafter described. A crimped portion of a ferrule made in accordance with the invention actually is of reduced interior perimeter and not merely fiattened or folded. By correctly shaping the coining areas of the dies and by using a crimping concavity of the optimum radius of curvature, the available forceof compression may be utilized efficiently "to compress the ferrule and the conductor therewithin into a substantially solid and integral mass, and the residual stresses are balanoed so that the contact surfaces do not spring back when the connection is released from the dies, but actually are held together under pressure such that a truly conductive connection is established.

The edge portions of the ferrule fold and are distorted outward in spaced local areas during the closing of the dies, and coining surfaces are pressed into the folds so re-distributing and workhardening the metal as to avoid release of the wire by re-opening.

In this specification and the accompanying drawings I have shown and described a preferred embodiment of my invention and variousmodifications thereof; but it is to be understood that these are not intended to be exhaustive nor limiting of the invention but, on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify and adapt it in various forms, each as may be best suited to the conditions of a particular use.

In the accompanying drawings, in which the invention is specifically illustrated:

'Figure "1 is a perspective view of an electrical connector attached to an electrical conductor in a manner embodying the invention;

Figure 2 is an elevational view, partly in section, of a rolled ferrule type electrical connector;

Figure '3 is an end view of the electrical connector illustrated in Figure '2 Figure 4 is an elevational view, partly in section, of a modified form of rolled ferrule type electrical connector;

Figure 5 is an end view of the electrical connector illustrated in Figure 4.;

Figure 6 is an elevational View, partly in section, of the electrical connector illustrated in Figures 2 and 3 positioned over the end of an electrical conductor and between the jaws formed by a pair of crimping dies;

Figure? is a plan view of the die surfaces of the lower die of Figure 6;

Figure 8 is a side elevation of the die of Figure '7';

Figure 9 is an elevational view similar to that of Figure 6 but showing the dies closed upon the electrical connector and crimping it onto the electrical conductor;

Figure 10 is a plan view of a crimped connector embodying the invention;

Figure 11 is a sectional view taken along the line ll--|l of Figure 10;

Figure 12 is a sectional view taken along the irregular line |2|2 of Figure 10;

Figure 13 is a plan view of a connector bearing, for purposes of illustration, a crimp not embodying the present invention;

Figure 14 is a sectional view taken along the line I l-l4 of Figure 13; and Figure 15 is a view similar to that of Figure 14 but showing, by way of further example, another crimp not embodying the present invention.

Figures 2 and 3 illustrate an electrical connector, generally indicated by 20, having a ferrule portion 2! and a terminal contact portion 22. Preferably the electrical connector is made of relatively soft, tinned copper; that is, of copper sufficiently soft to be readily coined between crimping dies but at the same time such that it will retain a permanent set impressed by the dies to maintain the high quality of the electrical connection. Fully annealed, pure, high-conductivity copper is advantageous in that it is readily formed as described and is work-hardened by the bending and coining so that it cannot be as readily deformed from its crimped condition.

Figures 4 and 5 illustrate a modified type of electrical connector which may be used in practicing the invention. In this instance the electrical connector, generally indicated by a, in-

cludes a ferrule portion Zia, a terminal contact portion 22a, and a seamless sleeve 23a positioned around the ferrule portion. Annular serrations or ridges 24a are provided, in some instances, on the interior of ferrule portion 2m to afford an anchor between the electrical connector and an electrical conductor.

It has been found advantageous in an electrical connector of this type to form the ferrule portion 2| a of dead soft, pure, ductile copper and to form the sleeve 23a of a relatively harder copper, so that the soft copper on the interior of the ferrule may be compressed with plastic flow into the fullest contact with every strand of the electrical connector and so that the metal will take a permanent set without serious spring back from the crimped condition, while the harder integumentary member will tend to restrain the deformation and thus to avoid opening of the seam of the inner ferrule.

Figure 6 illustrates the electrical connector of Figures 2 and 3 positioned over the end of an electrical conductor and caught between an upper die member 3! and a lower die member 32. Member 3! is provided with a concave die surface 33 while member 32 is provided with a concave die surface 34. These concave die surfaces lie, respectively, between upper fiat die surfaces 35 and lower fiat die surfaces 36 and each of said surfaces 33 and 34 has a chordal width approximately equal to the diameter of the electrical connector ferrule. As shown for example in-the drawing, the chordal dimension may be equal to the inside diameter of the ferrule; and it may vary from the over-all diameter of the ferrule portion of the connector to about three fourths of that diameter. (Note: In speaking of Width of the crimp or die, reference is being made to the horizontal dimension as shown in Figures 6 and 7, that is, the dimension crosswise O t e 'dentations (see Figure 15) or necking of the ferrule; in speaking of breadth of the crimp or die, reference is being made to the vertical dimension in Figure 7 and horizontal dimension in Figure 8, that is, longitudinally of the ferrule.) Beyond the fiat die surfaces there is provided on the upper die a pair of die stop portions 31 and on the lower die a pair of die stop portions 33, to be described in greater detail hereinafter.

Figure 9 illustrates the manner in which the concave die surfaces compress the electrical connector and conductor as die members 3| and 32 are brought toward one another during a crimping operation. The cross section and perimeter at the portion receiving the crimp are actually reduced and compressed; but the side portions of the ferrule, which lie between fiat die surfaces 35 and 36, do not actually receive very much direct compression from the flat die surfaces until the final movement of the die. That part of the force of compression which is concentrated at the portions of the ferrule which overlie and underlie the electrical conductor is directly utilized in compacting the strands of the conductor 50 and flowing the overlying and underlying portions of the ferrule into substantially perfect conformity with the contacted surfaces of the electrical conductor and to some extent in extruding metal of the ferrule from under the dies to the borders of the crimps.

With older types of crimping by dimple inferrule to smaller circumference, the closely packed wires around the exterior of the stranded conductor tend to form an arch or tube in which each wire is supported on the next, with the result that the strands of wire within such arch or tube are not satisfactorily compacted and corrosion easily enters the crimped area along the interstices between these wires. This tendenc is minimized by the application of the crimping forces according to the present invention, as will be described, so as to displace some of the outer wires and cause collapse of the arch. At the same time, the concave surfaces tend to limit the extent of collapse and confine the strands of the electrical conductor so that the wire is not merely flattened, as would be the case if it were hit with a hammer or clamped in a vise (see Fisures 13 and 14).

Although the shape of the crimp as shown in Figure 1 may appear difficult to form in a die, I have found that it can be simply achieved as described and claimed in my copending application, Serial No. 474,935, filed February 6, 1943. Briefly, the die is made by forming a cylindricallyshaped transverse groove, that is, a groove conforming to a portion of a cylindrical surface, in a simple dihedral angular die.

As best shown in Figures 7 and 8, each die member 3|, 32 tapers toward the die surfaces; hence, the concave die surfaces 33, 34 become broader as they become deeper due merely to the taper of the die stock. The radius of curvature of the concave surfaces 33', 34 is somewhat greater than the outside radius of the ferrules upon which the dies are to operate so that, as the dies close upon a ferrule, the broader portions first come into contact with the surface of the ferrule. Figrule along the seam where the butt edges of the ears of the rolled-up ferrule are brought together,

so as to support these edges and to aid in keeping them from separating. Due to this broader area, the initial pressure exerted for collapsing the arching of the stranded wire produces first a flattening of the dermis to elliptical form and then a collapse of any tube or arch of wire strands, and then coining of the die into the top and bottom portions of the ferrule, as seen in Figure 6, with consequent :flow of metal to the borders of the crimp area without excessive reduction in thickness at the center of the crimp area. When the chords of the arcuate surfaces of the opposed dies, i. e. surfaces 35 and 36 in Fig. 6, since they lie in the ohordal planes, are spaced by a distance twice the original thickness of the ferrule wall, the cross-sectional area within the ferrule between said arcuate surfaces should be at least as great, and advantageously very little greater than, the solid cross-sectional area of the wire. This is shown in Fig. 9 wherein the stranded wire has been compressed and the strands compacted into substantial conformity, :and the final movement of the dies isa-bout to begin in which the side portions of the ferrule between surfaces 35 and 36 will be compressed and extruded. In the final stage of the crimping (see Figure 9), the compression of the sides of the ferrule results in extrusion of metal from between the die surfaces at and beyond shoulders 40, 4!, 42, 43 and back into the elliptical space between the die surfaces 33 and 34, and at the same time in a readjustment of the metal in these side portions, which avoids any serious spring back-from the flattened form.

The relationships between the radius of curvature of the concave die surfaces 33 and 34 and the outside radius of the ferrule, as well .as the angle subtended by the concave dies, are important; and a change in such relationships may result in one crimp which differs from another in no apparently material regard but having"actually double the pull-out strength of the other crimp.

For maximum strength in the resulting crimp, the ratio of the radius of curvature :of the concave die surface to the outside radius of the ferrule should be greater than I, but small enough so that, when the distance between the flat die surfaces 3536 is equal to the doubled thickness of the ferrule wall, there is still sufficient space within the collapsed ferrule to contain the :solid cross-sectional area of wire 56. Obviously this limit depends upon the relation of the total solid cross section of the wire and the radius of the ferrule chosen to be crimped onto it. This choice, however, is not unlimited. If the ratio of radii becomes too great, that is, if the curvature of the die surfaces 33 and 34 becomes too fiat, the

holding power of the crimp will suffer. For best results I have used ratios on the range 1 to 1 /3 with best results at a "ratio of 1.4 to 1.5. Good results are obtained when the subtended arc of each concave die surface 33 and 34 is in the range from :about 60 to about 90. The best results have been obtained with an arc of about 85-90. correspondingly, the ohordal distance across the concave die surface (that is, the chord of its arc) should be about 1 to 2 times the length of theoutside radius of a ferrule to beacrimped'; but, as stated above, should advantageously 'be no less than the inside diameter of the ferrule. Finally, the best results have been attained when the cross-sectional area of the crimpedzsection (shown in Figure 9 between the dot and dash construc- 'tion lines), neglecting the copper extruded beyond the sides of the concave die segments 33 and 34, is, when the final coining step :is completed and stops 31-33 are brought together,

6 aboutsix tenthsof the initial cross-sectional area of the ferrule and wire before it was crimped. This relation is predetermined in the tool shown by the dimensions of the .stop portions 31, 3 8, but .it may obviously be determined in other ways.

It is to be [noted that the invention permits some latitude of sizes and shapes; that is, absolutely precise configurations are not-essential. It seems to suffice if the dimensions are kept within the general ranges specified. .-And correspondingly, "the crimp surface need not :follow a literally per-- feet are. The arcuate "shape appears to be best, but deviations therefrom :are permissible.

In :the :ordinary construction prior to my pres- :ent invention, if a ferrule were acollapsed or bent onto .a wirerafterthe "bendingor collapsing pressure :had been released the two ferrule cars would have a tendency :to spring back or reopen cutwardly along their fold-lines, so that the gripping action on the wires would be somewhat relaxed. Also, if the :two ferrule ears were "not connected together along their line of juncture, they would tend to open farther, by bending outwardly along their fold lines under stresses encountered during use.

As a feature of the present invention, the ferrule is crimped in such a way as to give a secure grip and maintain a pressure contact. For that purpose it is important that, except for the folded edges, the ferrule walls are spread to a larger radius of curvature so that the tendency to spring back imposes pressure on the engaged wires. The special treatment according to this invention largely obliterates the tendency to spring back at thefolded edges.

The ferrule is, in effect, corrugated on each face by a series of narrow flattened areas formed at spaced positions to give alternate fold sections 25 and 26 (see Figures 10l2) of different fold angles and thicknesses, as shown. This corrugation in itself gives rigidity; and beyond that it is my belief that the more acutely folded edges 21 have their tendency to spring back substan tially obliterated by the coining, which causes plastic flow .of the metal in the fold and thereby largely wipes out stress conditions in the metal which may have been left from the bending of the wall. The .same pressure which coins the exterior of the .ferrule under the die also produces coining on the interior so that the interior surface of the ferrule conforms more accurately to the surfaces of the wires. The coining at the exterior, moreover, by extruding metal from under the die, causes a thickening of the borders around the crimp, so that these areas as well as the metal on th interior of the ferrule and :in the wires, are stressed in compression; thus any tendency to recovery results in increase instead of diminution of the contact pressure. The strength of the crimp may also result, at least in part, from the fact that both the bend- .ing and the plastic flow effect a work-hardening in thesezones.

Two of the depressed areas 25 on each side of the ferrule are shown in the drawings spaced from the .sides and ends of said ferrule to leave the raised fold sections 26 at each end of the ferrule as well as between the two depressed areas 25 and to leave the bulges 2:1 at the sides of said ferrule. As a :result of this construction there is formed along each :folded side of the ferrule a continuous and modulated border rib which adds to the rigidity of the ;ferrule, and which thereby 7.:- ing of the opposed, depressed wire-gripping sections 25.

By way of comparison contrast the crimp of Figures l2 with that of 'Figures 13 and 14,

where the ferrule is simply flattened. The axis cent crimp 25a is not reinforced toward the sides 7 by longitudinal swaging of metal, as is the case with the crimp of Figure 102 The metal is caused to flow in my crimp into a bead surrounding the crimped surface; andthis head is stronger toward the folded portions of the crimp because of the increased longitudinal swaging of metal by the narrowing side die portions and wedge-like tool surfaces.

Figure shows'another type of crimped connection. Here, side walls 50 are drawn around crimp surface 251) by the dimple-type crimp impressed. During the crimping operation tensional stresses of considerable magnitude are set up in side walls 60. Any elastic return of metal following the drawing operation would loosen the grip of the crimp. My crimp is not dependent upon any such drawn construction It issecure because of a combined cold flow-and workhardening under compression. The reinforcing portions 28 and the bead around the crimp tend to maintain the compression. And in addition. it is effective through the entire cross section of the crimp so as to compact the wholeand thus preclude longitudinal seepage. of moisture and corrosion. But a crimp such as shownin' Figure 15 leaves a multiplicity of capillary-likeinterstices inviting deterioration, loss of holding power, and loss of electrical conductivity.

In the crimping operatiomit is desirable to form first one pair of opposed depressed areas 25, and then form the second adjoining pair. In this way the crimped area first formed is subjected to further compressive stress, as the result of the inherent resiliency of the ferrule metal, during the second crimping operation. This second crimping operation, therefore, imparts to said areas a more effective and corrosion resisting contact' Tests of sample terminals made by sectioning through the crimped area have shown that the metal of the ferrule and the metal of the wires within the ferrule are actually so pressed and fitted together that'no substantial 'voids are left between them; such perfection, however, is not necessary for many uses of theinventiomand good electrical connections may be made with a lesser compression of the wires. Such sectioning is illustrated in the-left-hand portion of Figure The right-hand half of this figure represents a section taken beyond the crimp.

Accelerated corrosion tests' have shown that with terminals made as described above under suitable crimping pressure, salt spray or other corrosive liquid does not penetrate into the crimped areas except 'as it may eat its way by the wires and ferrule,"particularly in: the case 8 where tinned wire is used, or where other coating of metal is present which exhibits a rela tively high plastic flow or difi'usion under the crimping pressure.

Another surprising advantage of the connection just described is in its extraordinarily high breaking strength. With an ordinary crimpedon terminal, the wire tends to be weakened so that it will break at the edge of the terminal with a pull very much below the normal tensile strength of the wire. With a single crimp, spaced at least one-sixteenth of an inch from "the end of the ferrule and the crimp made substantially as shown, the tensile strength as shown by pull test under vibration is approximately 90 per cent or more of the normal tensile strength of the wire, but this falls oil? rapidly as the edge of the crimp approaches closer than one-sixteenth of an inch to the edge of. the ferrule, dropping to 50 per cent or less if the crimp that on neither side of this line will the stock of the ferrule have to act with an effective cantilever arm greater than one-half the width-of the crimped ferrule.

The depressions 25 are preferably substantially elliptical or segmental in plan (that is, simulating the area between a chord and its are) except that the points may be cut off by short parallel sides 28, and are preferably arranged'as shown. This results in an actual coining of the metal with production of lateral bulges 2? in which the side areas of the metal are compressed solidly into said bulges 21, while the metal at the sections 28 between the two pairs of opposed depressions 25 and toward the ends of the ferrule retains a smooth elliptical cross section which, as described above, is reinforced by longitudinal extrusion of copper from the crimp areas. This construction also serves to afford optimum depressed areas 25 so as to grip effectively the wires 59, and to give maximum amounts of raised bead-like areas along the folded sides of the ferrule where it is needed most for rigidity.

The corrugations in the opposed facing surfaces of the ferrule formed by the alternate depressed and raised ferrule sections 25 and 26 serve not only to hold the ferrule as described against relaxing outwardly, but also serve to wrinkle the wires in the ferrule. This wrinkling of the wires assists in preventing said wires from being pulled out of the ferrule.

Figure 1 shows generally crimps 25, such as result from crimping operations as illustrated in Figures 6 and 9. The crimps there shown are only illustrative of my invention, however, and

one, two or more crimps may be used, depending upon the purposes for which the ferrule is intended. Likewise, the showing of Figures 6-9 is illustrative. The dies shown in Figures 6-9 may be closed together by any suitable mechanism,

power operated, or hand, or pedal operated.

As many modifications of the invention are possible and as many variations in the forms illustrated and described will be necessitated in adapting the invention to the many instances in which it may be used, the accompanying specification and drawings should not be construed in any way to limit the scope of the invention. The scope of the invention, on the contrary, is intended to be limited solely by the boundaries defined by the accompanying claims.

I claim:

1. An electrical connection having a ferrule and a contact section extending from said ferrule, said ferrule having transversely extending convex depressed areas on opposite faces thereof with radii of transverse curvature greater than the minor axis of the cross-section through the ferrule in said depressed areas, a conductor embraced by the ferrule in said depressed areas with surface conformity between the ferrule and conductor, portions of the ferrule beyond but bordering said depressed areas, including the side edge portions of the ferrule lying transversely beyond said curved faces of said opposite depressed areas, being of greater wall thickness than the wall thickness in said depressed areas.

2. An electrical connector as defined in claim 1 wherein the conductor has a substantially solid, lenticular cross-section lying substantially between said curved faces.

3. An electrical connection comprising an electrical conductor and the ferrule of an electrical connector embracing said conductor and having a crimp extending transversely across the ferrule forming a section therein of reduced crosssectional area with upper and lower convexly shaped depressed surfaces having chordal dimensions approximately equal to the quotient of the external perimeter of an uncrimped portion and a conducting contact section extending therei from, said ferrule being telescoped over the end of said stranded wire and joined thereto by opposed depressed convex areas relatively broad centrally, said depressed areas engaging said stranded wire between them, said depressed areas having narrower portions at their side edges, the sidemost ends of said depressed areas extending laterally substantially beyond adjacent undepressed portions of the ferrule, the radii of curvature in said convex depressed areas being substantially greater than the quotient of the periphery of the uncrimped portions of the ferrule divided by 2 pi and the angle subtended by the curve of each of said depressed areas being between 60 and 90, and said ferrule and wire being compacted into a substantial solid impervious mass within said depressed areas.

5. An electrical connector including a tubular ferrule, and an electrical conductor within the ferrule; the ferrule having a transversely extending portion tightly and intimately engaging the conductor therewithin, said portion being wider and having a smaller interior perimeter curvature between one and one-third and one and two-thirds times the quotient of the perimeter of the ferrule at a section spaced longitudinally from said portion divided by 2 pi, said curved faces each extending through arcs of from sixty to ninety degrees, the length of the chord across such are being one and one-third to two times said quotient, said curved faces being broader at their centers as measured longitudinally along the ferrule than at their ends, and the wall of the ferrule being thinner under opposite faces of said portion than the average wall thickness elsewhere in the ferrule and the ferrule walls laterally beyond said faces being thicker than said average.

6. In the art of connecting electrical conductors, that improvement which includes: forming a fiat connector blank, rolling a cylindrical ferrule bringing a butt seam therealong, positioning the ferrule over a section of the conductor, spreading a side centered in said butt seam and the opposite faces of the assembled ferrule and conductor to approximately cylindrical curvature of radius of from one and one-third to one and two-thirds times the outside radius of the cylindrical ferrule and over a chordal width across said curvature not more than the outside diameter of the cylindrical ferrule and not less than one and one-third times the outside radius of the cylindrical ferrule, forcing said spread faces toward one another and thereby flattening and consolidating the conductor within the ferrule ,while supporting said spread faces against deformation but leaving unsupported side portions between said faces, whereby the ferrule metal bulges and extrudes laterally from the wall portion between said spread faces and until the distance between said opposite faces is about double the original thickness of the ferrule wall, and confining said laterally extruded ferrule metal to thespace between the chordal planes of said spread faces until the metal portions therebetween have been reduced to a total thickness substantially less than twice the thickness of the uncrimped ferrule wall.

STEPHEN N. BUCHANAN.

REFERENCES CITED The following references are of record in the file of this patent:

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